1. Field of the Invention
The present invention relates to a clamp for optical fibers used in an apparatus which manufacturers optical fiber couplers for communication systems and sensor systems.
2. Description of the Art
An important component in configuring optical communication systems and optical data link networks is an optical splitter to distribute the optical signal from the light source with a desired ratio. One such optical splitter is constructed of a number of fiber couplers melted together with heat and then drawn under a predetermined tensile force. For the melting process, the glass portions of the optical fibers must be parallel and are so held with a clamp mechanism. The accuracy of the clamp's position greatly influences the characteristics of manufactured optical fiber coupler.
Conventional clamps, as disclosed in Japanese Patent Preliminary Publication No. 63-118705, hold the optical fibers in two directions. FIG. 1 is a perspective view of a clamp described in JP No. 63-118705. Two optical fibers 3 and 4 are held in a vertical direction by a clamp 32. The vertically aligned fibers are then held in a horizontal direction by a horizontal position adjusting device.
The clamp in FIG. 1 consists of two axially spaced clamps that combined, hold the fibers in the vertical and horizontal directions while clamping the fibers in a twisted form. If the height of the slot in clamp 32 is greater than the diameters of the optical fibers 3 and 4, the fibers will no be placed in proper position within the slot, as shown in FIG. 2, thereby making it difficult to horizontally align the fibers side-by-side.
FIG. 3 shows two position adjusting devices 30 and 31. One adjusting device 30 for the horizontal position and the adjusting device 31 for the vertical position. In this configuration, one of the adjusting devices tends to clamp the fibers 3 and 4 before the other adjusting device clamps the fibers. If the horizontal position adjusting device 30 is the first to clamp the fibers, it is possible that the fibers will look like that shown in FIG. 4B rather than that shown in FIG. 4A.
After the horizontal adjusting device is in position, adjusting device 31 clamps the fibers so that the fibers clamped by the device 30 are like that in FIG. 4C while the fibers clamped by the device 31 are like that in FIG. 4D. The two optical fibers continue to be improperly axially positioned. The result is the same when the vertical adjusting device 31 clamps the optical fibers first. It is difficult, therefore, to have the optical fibers properly clamped using the conventional ways of clamping shown in FIGS. 1 and 3.
Meanwhile Japanese Utility model Preliminary Publication No. 1-94904 discloses an optical fiber fixing device which uses a pair of optical fiber sandwiching devices having a thickness and a level difference smaller than the diameter of the optical fibers and greater than the radius. However, this fiber fixing device is not easy to use.
Japanese patent Preliminary Publication No. 64-80913 discloses an optical fiber fixing device where the two optical fibers are received in the V-shaped slot of each of the two halves of a block. The two halves of the block are put together such that the two fibers are pressed against each other for a closely sandwiched condition.
The depth of the V-shaped slot cannot be made greater than the diameter of the two optical fibers 3 and 4. Otherwise, the optical fibers 3 and 4 will no be in contact with each other correctly when the two halves of block are put together, as shown in FIG. 5A.
In FIG. 5A, the angle of the V-shaped slot is 90 degrees. For the fibers to be sandwiched together properly, the possible maximum width M of the opening of V-shaped slot is given 2(1+.sqroot.2)r where r is the radius of the optical fibers. Therefore, the possible maximum width D of the V-shaped slot shown in FIG. 5C is M, as shown in FIG. 5B, wherein D is defined by 2(1+.sqroot.2)r. If the diameter 2r of the optical fiber is 125 .mu.m, then M is approximately 600 .mu.m.
As a practical matter, the opening width D of the V-shaped slot is in the range of 200 to 300 .mu.m, which is very small. Consequently, the operation of inserting an optical fiber into the V-shaped slot must be performed under a microscope.
Since the two optical fibers tend to curl, it is quite rare that the two optical fibers are held perfectly parallel by the V-shaped slot. The device disclosed by Japanese Patent Preliminary Publication No. 64-80913 requires an operator to ensure that the optical fibers are completely inserted into the V-shaped slot. This operation is carried out under a microscope, which causes fatigue of the operator's eyes.